1. Field of the Invention
The present invention relates to a method for fabricating nano material pattern.
2. Description of the Related Art
Indium tin oxide (ITO), one of the representative transparent electrode materials, has been widely applied to a variety of devices including liquid crystal display, organic light emitting display, touch screen, electroluminescent device, and photoelectric cell, etc. As the area of flat display gets larger, sheet resistance becomes a problem of the conventional ITO applied thereto. When ITO is applied to flexible display, cracks happen to be developed, which limits the use of ITO.
To overcome the above problem, an alternative for ITO such as metal nano wire, carbon nano tube, graphene, and conducting polymer has been tried and a technique to use a metal thin film with a mesh pattern is under development.
Such materials as metal nano wire, carbon nano tube, and graphene are used as the form of dispersion which can be prepared by dispersing the said material in a specific solvent, in order to make a film. At this time, the method for fabrication of a pattern based on such dispersion is limited.
The conventional method for fabrication of a specific material pattern based on dispersion is composed of the following processes: spraying the dispersion to a material for coating; and etching the coated material to form a pattern. For example, Korean Patent Publication No. 10-2013-0048717 describes the nanowire-based transparent conductors and methods of patterning same. Particularly, that invention is related to the partial etching to form low-visible or invisible patterns.
There is another invention related to the method for preparing nano wire comprising the steps of oxidizing copper nano wire by laser irradiation; and reducing the oxidized copper nano wire to generate the sintered nano wire, and the method for fabrication of nano wire pattern (Korean Patent No. 10-1357179). The method comprising the steps of coating patterned mold with silver nano wire and directly transcribing the coated silver nano wire on the substrate has also been reported (Nano. Res., 3, 564, 2010). Another example is the method for fabrication of a pattern by treating the substrate partially with dopamine to increase hydrophilicity (ACS Appl. Mater. Interfaces., 4, 1855, 2012).
The most common method used in the semiconductor manufacturing process, so called ‘lift-off’, is characterized by the steps of forming a photoresist pattern on a substrate via photolithography; and then eliminating the photoresist by coating the substrate with a material requiring fabrication. However, the dispersion can hardly be used in the next procedure. The disadvantages of the method are firstly difficulty in photoresist patterning on an organic substrate and secondly elimination of the photoresist pattern by a specific solvent used as the dispersion (for example, IPA, ethanol, etc). Even if the photoresist pattern is not eliminated somehow, nano material such as nano wire can be separated by a solvent such as acetone during the elimination process of photoresist pattern, which is also a problem.
Therefore, when fabricating a material in a dispersion is induced according to the method of lift-off, it is not supposed for the dispersion solvent to eliminate a polymer pattern formed on an organic substrate and it is not supposed for the polymer pattern to react with nano material like nano wire in order to prevent the nano material from being off from the substrate. The solvent that eliminates the patterned polymer should not affect the organic substrate.
In the course of studying a method for fabricating nano material pattern that can satisfy the above conditions, the present inventors succeeded in forming a polymer pattern by applying perfluorinated polymer on a substrate and accordingly developed a method for fabricating nano material pattern by using the dispersion prepared by spraying nano material on the formed polymer pattern, leading to the completion of this invention.